Semiconductor devices with a so-called MOS (“Metal-Oxide-Semiconductor”) structure have conventionally been known. The semiconductor devices with the MOS structure (hereinafter referred to as “MOS-type semiconductor devices”) include, for example, IGBTs (“Insulated Gate Bipolar Transistors”) and MOSFETs (“MOS Field Effect Transistors”).
Conventional MOS-type semiconductor devices include series-connected Zener diodes provided as overvoltage protection measures. Specifically, a Zener diode that is designed to break down at a voltage lower than the breakdown voltage of an MOS-type semiconductor device is disposed between the collector and the gate of the MOS-type semiconductor device (for example, see Patent Literature 1).
In order to ensure a breakdown voltage, the MOS-type semiconductor device has a voltage supporting region in a peripheral portion of a semiconductor substrate, and a conductor portion (which is called “field plate”) is disposed along the voltage supporting region. The conductor portion is disposed on an insulating film located on the semiconductor substrate. This stabilizes the surface potential of the voltage supporting region to improve the reliability of the semiconductor device.